1. Field of the Invention
The present invention relates to a front panel for a display device (hereafter, referred to a display front panel), specifically, relates to a display front panel having an anti-reflection layer for improving the visibility of the display image.
2. Description of the Prior Art
In recent years, a projection television of back projection system and a plasma display television have been used as an image system suited for a larger screen instead of cathode-ray tube (CRT) television. Further, widening of liquid crystal display has been advanced. These displays may often be attached with a front panel for protecting a screen. On a front panel, a hard coat layer comprising a crosslinked polymer is provided to prevent scratch on a surface. Further, in order to enhance a contrast of a screen image, dye or pigment may be added to reduce a transmittance of visible rays.
Since projection televisions, plasma display televisions, and liquid crystal displays are large in size and flat, they receive more reflection images of environmental objects and person on the screen thereof than conventional CRT displays. In addition, since a brightness of an image on the said displays is smaller than that on conventional CRT displays, reflection images of environmental objects will decrease the visibility of the image. Further, scratch-protection ability is required for a display front panel having a function as a protection plate. In addition, in order to enhance a contrast of an image, dye or pigment may be added to a resinous base material to form a display front panel. This reduces a transmittance of visible rays and, accordingly, there is a limitation in the amount of additive such as dye or pigment.
In resent years, cellular phones have been popularized and many functions other than calling function have been added to them. FIG. 1 shows a perspective view of typical figure of a cellular phone consisting of a display window 1, a control unit 3, an antenna 4 and the like. Many kinds of information such as telephone numbers, mail information and the like are displayed on the display window 1 of the cellular phone, and the display size has been increased gradually. Further, a color display has begun to be popularized. On this display window, a transparent resin plate is generally used as the protective plate and in order to prevent a scratch on the surface, a hard coat layer comprising a crosslinked polymer is provided generally.
An anti-reflection layer, which is provided by laminating a layer having a high optical refractive index value and a layer having a low optical refractive index value in this order over the surface of the base plate, has been known. Here, the layer having a high optical refractive index value has a larger optical refractive index value than that of the base plate and the layer having a low optical refractive index value has a smaller optical refractive index value than that of the layer having a high optical refractive index value. The layer having a high optical refractive index value and the layer having a low optical refractive index value in combination constitute an anti-reflection layer. The layer having a high optical refractive index value and the layer having a low optical refractive index value are usually adjusted in thickness in a way that the optical film thickness (nxc3x97d) i.e. the product of an optical refractive index value (n) and a thickness (d) of these layers, are about xc2xc and about xc2xd of the wavelength (xcex) of the visible rays, respectively.
Here, as a layer having a high optical refractive index value, a layer has been known in which a layer is formed by applying and curing a coating composition material on the surface of the base plate. As a composition material for coating, a composition material comprising a compound having two or more unsaturated double bonds in a molecule and metal alkoxide has been known (JP-A-8-297201).
As a layer having a low optical refractive index value, a layer comprising a cured organo-silicon compound has been known (JP-A-63-4201).
However,-the anti-reflection plate, where an anti-reflection layer consisting of layers of both high and low optical refractive index values are provided on the surface of the base plate, is poor in scratch-protection ability and the anti-reflection layer tends to be peeled out.
Accordingly, the present invention is intended to provide a display front panel to be used for a projection television, a plasma display television, a liquid crystal display, or a cellular phone display, etc. with little reflection images of environmental objects, with an improved visibility of image, and with excellent scratch-protection ability.
As a result of extensive studies by the inventors, it has been found that reflection images of environmental objects and persons can be reduced when an anti-reflection layer as described hereinafter is provided on at least one surface of a display front panel. Further, it has been found that hardness of a front panel is improved along with its visibility by providing an anti-reflection layer comprising at least two layers disposed on the surface of a base plate of a front panel wherein a first layer facing the surface of the base plate of the display front panel has a larger optical refractive index value than that of a second layer which is overlaid on the first layer. Particularly, when the first layer having a larger optical refractive index value is a cured film made of a composition containing (A) a polymerizable compound or an oligomer thereof having at least two unsaturated double bonds and being capable of polymerizing by the irradiation of activated energy beams, (B) an organo-silicon compound or an oligomer thereof and (C) particles of metal oxide selected from the group consisting of zirconium dioxide, titanium dioxide, tin dioxide and antimony dioxide, and the second layer having a smaller optical refractive index value is made of a cured organo-silicon compound, are provided, thus a display front panel having not only anti-reflective property but also sufficient scratch-protection ability is obtained.
By providing such an anti-reflection layer, a transmittance of visible rays becomes larger, consequently, an additional amount of dye or pigment can be added to the base plate of the display front panel resulting in an improved contrast of a screen image.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.